When you scroll in out on the ranking graph it affects both the x and y axis, but when you scroll in it only affects the x axis. I find this a little annoying personally but I imagine there are people who are on the other side of the fence.
Hello, I took the time to investigate this, because I did not even know that you could zoom in and out on the rank graph.
When I zoomed in, the x-axis and y-axis both changed accordingly.
Next I zoomed out as far as possible and nothing strange happened.
After which I zoomed in as far as possible, this is where something was weird for me. As I zoomed back out, all of the lines remained horizontal for some time. It seemed that only the y-axis was zooming out. This continued until the y-axis was once again at its maximum length. Then I could not zoom out any more and the lines were still horizontal. With a bit of random zoom in and out the x-axis once again was changing appropriately.